The torque rod or radius rod system in a transit bus is a crucial element in the bus suspension system and provides the securing interface between the chassis and the bus body, which are also connected to the axle by the bus shock absorber and leaf spring system. [Fleet Equipment, July, 1985, pages 65,66 ] The rod provides a secure connection between the chassis and frame or body and maintains the alignment of fixed points in the two members. In the prior art the torque rod or radius rod is a rod having bushings at two opposite ends. Typically the bushing comprises a split metal ring insert surrounded by a compressed rubber interface enclosed within the integrally cast circumferential end of the rod. The bushing is subjected to continual internal stress because the bushing/rubber/rod assembly is designed to be maintained in fixed relationship. Forces are absorbed into the rubber interface, and the twisting actions are absorbed by the rubber's elastic properties. The rubber interface resists both rotation and conical movement of the ring with respect to the torque rod. Typically, this design provides a rotation of +/-15 degrees and a conical angle of +/-5 degrees. Once the split ring becomes moveable, the ring will rotate and erode the surrounding rubber, eventually rendering the rod ineffective.
Transit buses usually include multiple torque rods, from 6 to 12 per bus, and because the rods are subjected to considerable strees, breakdown is frequent; however, replacement is a difficult and labor intensive job. For example, many garages schedule the replacement of a single torque rod for 4.5 hours of labor which involves the difficult task of installing the rod over a dowel in an interference fit and aligining the two supported points of the rod.